Display paging receivers are widely used for information transfer. A goal of pager designers is to reduce the size and cost of each pager while working within the constraint that a pager must minimize its energy consumption due to limited battery power.
To display received information, pagers typically utilize displays which are capable of presenting alphanumeric data and messages of various lengths. In an effort to effectively display information and meet pager design goals, a liquid crystal display (LCD) is generally used. The LCD display is utilized because it has substantial flexibility in the format and presentation of messages, it is extremely compact, and it consumes very little power.
The LCD display forms letters, symbols, and numerals on the display by producing contrasts on certain portions of the display screen. These contrasting portions of the display screen, however, are only viewable if the display is illuminated by sufficient ambient light, reflected light, or supplemental backlight provided behind the display. Messages may be read on the LCD display in a low ambient light environment only if the pager provides supplemental backlight illumination to make the contrasting portions of the LCD display readable.
Various methods for providing supplemental backlight illumination to the LCD display have been proposed. The simplest method is to provide a separate switch on the pager which exclusively controls the illumination of an incandescent lamp or electro-luminescence backplane under the LCD display. Other methods are known for automatically activating this type of light or backplane using a photosensor which monitors the ambient light levels and automatically activates a light in response to low ambient light conditions.
These known methods of illuminating a pager display burden the pager with additional components which increase both the pager size requirements and the cost of the pager. Therefore, in order to reduce the size and cost of the pager, it would be desirable to provide a visual display pager that minimizes the number of components needed to operate the illumination device.
Additionally, certain illumination display circuits automatically activate the illumination feature under conditions where the display is readable or deactivate the illumination feature under conditions where the display is unreadable. These automatic illumination features do not respond to the individual pager user's needs for display illumination. Thus, it would be desirable for display illumination to be exclusively controlled by the pager user.